Cardiac rhythm management system with user interface for threshold test

ABSTRACT

An implantable cardiac rhythm management system includes a user interface, such as an external programmer, for performing therapy energy threshold tests. The threshold tests allow the caregiver to determine the threshold energy at which paces capture the heart, i.e., cause a resulting contraction of the heart chamber to which the paces are delivered. The programmer provides recorded indications of the energy corresponding to each paced event, so that the caregiver can easily determine the point at which capture was lost. This recorded representation of pacing energy makes it easy for the caregiver to determine proper pacing thresholds to be used to ensure adequate pacing, while minimizing energy drain to prolong the useful life of the implanted device.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.11/427,404 (Atty. Docket No. 279.199US4), filed on Jun. 29, 2006, whichis a continuation of U.S. patent application Ser. No. 10/692,295 (Atty.Docket No. 279.199US3), filed on Oct. 23, 2003, now issued as U.S. Pat.No. 7,096,065, which is a continuation of U.S. patent application Ser.No. 10/021,861 (Atty. Docket No. 279.199US2), filed on Dec. 17, 2001,now issued as U.S. Pat. No. 6,671,551, which is a continuation of U.S.patent application Ser. No. 09/378,106 (Atty. Docket No. 279.199US1),filed on Aug. 20, 1999, now issued as U.S. Pat. No. 6,353,761, priorityto all of which is hereby claimed, and all of which are herebyincorporated by reference in their respective entireties.

TECHNICAL FIELD

The present system relates generally to cardiac rhythm managementsystems and particularly, but not by way of limitation, to a cardiacrhythm management system providing, among other things, a user interfacefor threshold testing.

BACKGROUND

When functioning properly, the human heart maintains its own intrinsicrhythm, and is capable of pumping adequate blood throughout the body'scirculatory system. However, some people have irregular cardiac rhythms,referred to as cardiac arrhythmias. Such arrhythmias result indiminished blood circulation. One mode of treating cardiac arrhythmiasuses drug therapy. Anti-arrhythmic drugs are often effective atrestoring normal heart rhythms. However, drug therapy is not alwayseffective for treating arrhythmias of certain patients. For suchpatients, an alternative mode of treatment is needed. One suchalternative mode of treatment includes the use of a cardiac rhythmmanagement system. Such systems often include portions that areimplanted in the patient and deliver therapy to the heart.

Cardiac rhythm management systems include, among other things,pacemakers, also referred to as pacers. Pacers deliver timed sequencesof low energy electrical stimuli, called pace pulses, to the heart, suchas via an intravascular leadwire or catheter (referred to as a “lead”)having one or more electrodes disposed in or about the heart. Heartcontractions are initiated in response to such pace pulses (this isreferred to as “capturing” the heart). By properly timing the deliveryof pace pulses, the heart can be induced to contract in proper rhythm,greatly improving its efficiency as a pump. Pacers are often used totreat patients with bradyarrhythmias, that is, hearts that beat tooslowly, or irregularly.

Cardiac rhythm management systems also include cardioverters ordefibrillators that are capable of delivering higher energy electricalstimuli to the heart. Defibrillators are often used to treat patientswith tachyarrhythmias, that is, hearts that beat too quickly. Suchtoo-fast heart rhythms also cause diminished blood circulation becausethe heart isn't allowed sufficient time to fill with blood beforecontracting to expel the blood. Such pumping by the heart isinefficient. A defibrillator is capable of delivering a high energyelectrical stimulus that is sometimes referred to as a defibrillationcountershock. The countershock interrupts the tachyarrhythmia, allowingthe heart to reestablish a normal rhythm for the efficient pumping ofblood. In addition to pacers, cardiac rhythm management systems alsoinclude, among other things, pacer/defibrillators that combine thefunctions of pacers and defibrillators, and any other implantable orexternal systems or devices for diagnosing or treating cardiacarrhythmias.

One problem faced by cardiac rhythm management systems is determiningwhether the therapy delivered has had its desired effect. For example,after implanting a pacer in a patient, a physician or other caregiverwould like to know if the pace pulses being delivered are effective at“capturing the heart,” i.e., evoking a contraction of the heart chamberto which the pace pulse was delivered. If the paces are not succeedingat capturing the heart, the physician will likely program a higherenergy pace pulse to obtain capture. In order to save energy, prolongingthe useful life of the implanted device before replacement is required,lower energy paces are preferable provided that the physician is assuredthat the lower energy pace pulses will capture the heart. Replacement ofthe implanted device carries significant expense as well as some risk ofdiscomfort and/or complications.

In order to determine the appropriate energy of pacing therapy, thephysician typically programs several different therapy energy levels(i.e., pacing voltage amplitude, pacing pulsewidth, or combination ofamplitude and pulsewidth) to see what energy levels appropriately obtaincapture. Because proper therapy energy levels are critical in providingeffective cardiac rhythm management therapy and extending the usefullife of the implanted device, there is a need for techniques that assistthe physician or other caregiver in determining threshold energies forcardiac rhythm management therapy.

SUMMARY OF THE INVENTION

This document describes, among other things, portions of cardiac rhythmmanagement system including a user interface for performing therapyenergy threshold tests. In one embodiment, the user interface includes aprogrammer that provides recorded indications of the energycorresponding to paced events, so that the caregiver can easilydetermine the point at which capture was lost. This recordedrepresentation of pacing energy makes it easy for the caregiver todetermine proper pacing thresholds to be used to ensure adequate pacing,while minimizing energy drain to prolong the useful life of theimplanted device.

In one embodiment, the cardiac rhythm management system includes anexternal user interface. The user interface includes a communicationmodule, adapted for remote communicative coupling to the implantabledevice. The user interface also includes a threshold testing module. Theuser interface provides a recorded output indicator of energy associatedwith an instance of therapy delivery by the implantable device.

This document also describes a method that includes pacing a patient atvarying energies and recording a separate output indicator of energyassociated with each pace. These and other aspects of the present systemand methods will become apparent upon reading the following detaileddescription and viewing the accompanying drawings that form a partthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like numerals describe substantially similar componentsthroughout the several views Like numerals having different lettersuffixes represent different instances of substantially similarcomponents.

FIG. 1 is a schematic drawing illustrating generally one embodiment ofportions of a cardiac rhythm management system and an environment inwhich it is used.

FIG. 2 is a schematic drawing illustrating generally one embodiment of acardiac rhythm management device coupled by leads to a heart.

FIG. 3 is a schematic diagram illustrating generally one embodiment ofportions of a cardiac rhythm management device coupled to heart.

FIG. 4 illustrates generally one embodiment of a screen displayassociated with an external programmer or other user interface.

FIG. 5 is an example of a strip chart recording provided by a printerassociated with a programmer.

FIG. 6 is an example of a strip chart recording, similar to FIG. 5, inwhich the output indicators provide recorded indications of pacingpulsewidth, rather than amplitude, during pacing threshold testing.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims and their equivalents. In thedrawings, like numerals describe substantially similar componentsthroughout the several views Like numerals having different lettersuffixes represent different instances of substantially similarcomponents. In this document, “and/or” refers to non-exclusive “or”(e.g., “A and/or B” includes each of “A but not B,” “B but not A,” and“A and B”).

The present methods and apparatus will be described in applicationsinvolving implantable medical devices including, but not limited to,implantable cardiac rhythm management systems such as pacemakers,cardioverter/defibrillators, pacer/defibrillators, and biventricular orother multi-site coordination devices. However, it is understood thatthe present methods and apparatus may be employed in unimplanteddevices, including, but not limited to, external pacemakers,cardioverter/defibrillators, pacer/defibrillators, biventricular orother multi-site coordination devices, monitors, programmers andrecorders.

General System Overview and Examples

This document describes, among other things, a cardiac rhythm managementsystem with a user interface for a threshold test. FIG. 1 is a schematicdrawing illustrating generally, by way of example, but not by way oflimitation, one embodiment of portions of a cardiac rhythm managementsystem 100 and an environment in which it is used. In FIG. 1, system 100includes an implantable cardiac rhythm management device 105, alsoreferred to as an electronics unit, which is coupled by an intravascularendocardial lead 110, or other lead, to a heart 115 of patient 120.System 100 also includes an external user interface, such as programmer125, providing wireless communication with device 105 using acommunication module such as telemetry device 130. Catheter lead 110includes a proximal end 135, which is coupled to device 105, and adistal end 140, which is coupled to one or more portions of heart 115.

FIG. 2 is a schematic drawing illustrating generally, by way of example,but not by way of limitation, one embodiment of device 105 coupled byleads 110A-B to heart 115, which includes a right atrium 200A, a leftatrium 200B, a right ventricle 205A, a left ventricle 205B, and acoronary sinus 220 extending from right atrium 200A. In this embodiment,atrial lead 110A includes electrodes (electrical contacts) disposed in,around, or near an atrium 200 of heart 115, such as ring electrode 225and tip electrode 230, for sensing signals and/or delivering pacingtherapy to the atrium 200. Lead 110A optionally also includes additionalelectrodes, such as for delivering atrial and/or ventricularcardioversion/defibrillation and/or pacing therapy to heart 115.

In FIG. 2, a ventricular lead 110B includes one or more electrodes, suchas tip electrode 235 and ring electrode 240, for delivering sensingsignals and/or delivering pacing therapy. Lead 110B optionally alsoincludes additional electrodes, such as for delivering atrial and/orventricular cardioversion/defibrillation and/or pacing therapy to heart115. Device 105 includes components that are enclosed in ahermetically-sealed can 250. Additional electrodes may be located on thecan 250, or on an insulating header 255, or on other portions of device105, for providing unipolar pacing and/or defibrillation energy inconjunction with the electrodes disposed on or around heart 115. Otherforms of electrodes include meshes and patches which may be applied toportions of heart 115 or which may be implanted in other areas of thebody to help “steer” electrical currents produced by device 105. In oneembodiment, one of atrial lead 110A or ventricular lead 110B is omitted,i.e., a “single chamber” device is provided, rather than the dualchamber device illustrated in FIG. 2. In another embodiment, additionalleads are provided for coupling device 105 to other heart chambersand/or other locations in the same heart chamber as one or more of leads110A-B. The present method and apparatus will work in a variety ofconfigurations and with a variety of electrical contacts or“electrodes.”

Example Cardiac Rhythm Management Device

FIG. 3 is a schematic diagram illustrating generally, by way of example,but not by way of limitation, one embodiment of portions of device 105,which is coupled to heart 115. Device 105 includes a power source 300,an atrial sensing circuit 305, an atrial therapy circuit 310, aventricular sensing circuit 315, a ventricular therapy circuit 320, anda controller 325.

Atrial sensing circuit 305 is coupled by atrial lead 110A to heart 115for receiving, sensing, and/or detecting electrical atrial heartsignals. Such atrial heart signals include atrial activations (alsoreferred to as atrial depolarizations or P-waves), which correspond toatrial contractions. Such atrial heart signals include normal atrialrhythms, and abnormal atrial rhythms including atrial tachyarrhythmias,such as atrial fibrillation, and other atrial activity. Atrial sensingcircuit 305 provides one or more signals to controller 325, via node/bus327, based on the received atrial heart signals.

In one embodiment, atrial therapy circuit 310 provides atrial pacingtherapy, as appropriate, to electrodes located at or near one of theatria 200 of heart 115 for obtaining resulting evoked atrialdepolarizations. In a further embodiment, atrial therapy circuit 310also provides cardioversion/defibrillation therapy, as appropriate, toelectrodes located at or near one of the atria 200 of heart 115, forterminating atrial fibrillation and/or other atrial tachyarrhythmias.

Ventricular sensing circuit 315 is coupled by ventricular lead 110B toheart 115 for receiving, sensing, and/or detecting electricalventricular heart signals, such as ventricular activations (alsoreferred to as ventricular depolarizations or R-waves), which correspondto ventricular contractions. Such ventricular heart signals includenormal ventricular rhythms, and abnormal ventricular rhythms, includingventricular tachyarrhythmias, such as ventricular fibrillation, andother ventricular activity. Ventricular sensing circuit 315 provides oneor more signals to controller 325, via node/bus 327, based on thereceived ventricular heart signals.

In one embodiment, ventricular therapy circuit 320 provides ventricularpacing therapy, as appropriate, to electrodes located at or near one ofthe ventricles 205 of heart 115 for obtaining resulting evokedventricular depolarizations. In a further embodiment, ventriculartherapy circuit 320 also provides cardioversion/defibrillation therapy,as appropriate, to electrodes located at or near one of the ventricles205 of heart 115, for terminating ventricular fibrillation and/or otherventricular tachyarrhythmias.

Controller 325 controls the delivery of therapy by atrial therapycircuit and/or ventricular therapy circuit 320 and/or other circuits,based on heart activity signals received from atrial sensing circuit 305and ventricular sensing circuit 315, as discussed below. Controller 325includes various modules, which are implemented either in hardware or asone or more sequences of steps carried out on a microprocessor or othercontroller. Such modules are illustrated separately for conceptualclarity; it is understood that the various modules of controller 325need not be separately embodied, but may be combined and/or otherwiseimplemented, such as in software/firmware.

In general terms, sensing circuits 305 and 315 sense electrical signalsfrom heart tissue in contact with the catheter leads 110A-B to whichthese sensing circuits 305 and 315 are coupled. Sensing circuits 305 and315 and/or controller 325 process these sensed signals. Based on thesesensed signals, controller 325 issues control signals to therapycircuits, such as ventricular therapy circuit 320, if necessary, for thedelivery of electrical energy (e.g., pacing and/or defibrillationpulses) to the appropriate electrodes of leads 110A-B. Controller 325may include a microprocessor or other controller for execution ofsoftware and/or firmware instructions. The software of controller 325may be modified (e.g., by remote external programmer 125) to providedifferent parameters, modes, and/or functions for the implantable device105 or to adapt or improve performance of device 105.

In one further embodiment, one or more sensors, such as sensor 330, mayserve as inputs to controller 325 for adjusting the rate at which pacingor other therapy is delivered to heart 115. One such sensor 330 includesan accelerometer that provides an input to controller 325 indicatingincreases and decreases in physical activity, for which controller 325increases and decreases pacing rate, respectively. Another such sensorincludes an impedance measurement, obtained from body electrodes, whichprovides an indication of increases and decreases in the patient'srespiration, for example, for which controller 325 increases anddecreases pacing rate, respectively. Any other sensor 330 providing anindicated pacing rate can be used.

Example Threshold Test

Device 105 includes, among other things, a pacing threshold test moduleincluded in software and/or hardware of controller 325. Using an icon onthe screen display of external programmer 125, the physician or othercaregiver initiates a pacing threshold test mode that allows observationof the effectiveness of varying therapy energy levels at capturing theheart, i.e., at obtaining a resulting contraction of the heart chamberto which the energy is delivered. Energy levels are varied by changingeither the amplitude or the pulsewidth of the delivered pacing pulse.During the threshold test, data is communicated from the implanteddevice 105 to the external user interface, e.g., programmer 125, usingreal-time telemetry by device 105 in response to synchronization pulsesprovided by programmer 125.

In one embodiment, amplitude is varied by changing the pacing amplitudeto 5.0V for four paces, then stepping the energy down by 0.5V incrementsfor each successive four paces down to a pacing amplitude of 3.0V. Afterthat, the pacing amplitude continues to decrease by 0.2V increments, foreach successive four paces, until the pacing amplitude reaches 0.2V. Asthe pacing amplitudes are decreased, the caregiver observes on thescreen display of programmer 125 a corresponding electrogram signal,i.e., a cardiac signal associated with the particular chamber of theheart to which the pace pulses are delivered. If the caregiver noticesthat the pacing pulses being delivered fail to capture the heart (i.e.,the characteristic depolarization is absent after the pace pulse isdelivered), the caregiver ends the threshold test, such as by using anicon on the user interface. When the caregiver ends the threshold test,the user interface displays the last pacing amplitude delivered beforecapture was lost. The caregiver can then set the pacing amplitude tothat value, or alternatively, the caregiver can add an appropriate“safety margin” when setting the pacing amplitude.

During the pacing threshold test, the previously programmed pacingparameters (amplitude, pulsewidth, rate, AV delay, etc.) are stored. Inone embodiment, after the pacing threshold test is ended, pacingcontinues at either the previously stored pacing parameter values, or atdefault values that are regarded as safe enough to ensure capture (e.g.,5.0V amplitude, 0.5 millisecond pulsewidth). After a pacing thresholdtest is conducted for a particular chamber, the caregiver can retestpacing amplitudes. In one embodiment, a retest of pacing thresholdsbegins at the default initial values (e.g., amplitude of 5.0V orpulsewidth of 0.5 milliseconds). In another embodiment, however, aretest of pacing thresholds begins at a predetermined number ofincrements (e.g., 3 increments) above the energy level before whichcapture was lost. For example, if a first threshold test usingamplitudes lost capture at 0.4V, as determined by the physician endingthe threshold test, then, the screen display would indicate 0.6V as thethreshold voltage before which capture was lost. In this example, aretest of pacing thresholds would begin at 1.2V, that is, at 3increments of 0.2V above the previous minimum capture amplitude of 0.6V.By starting a retest of pacing thresholds at a predetermined number ofincrements above the result of the previous test, the time required forconducting a retest is reduced.

In one embodiment, the pacing amplitudes or pulsewidths areautomatically stepped down (decremented) every fourth pace. In anotherembodiment, the pacing amplitudes or pulsewidths are manuallydecremented or incremented by the physician using the “+” and “−” iconson the screen display of programmer 125 and illustrated in FIG. 4.

Example Programmer Interface

FIG. 4 illustrates generally, by way of example, but not by way oflimitation, one embodiment of a screen display associated with externalprogrammer 125. The screen display of FIG. 4 includes visual images ofcardiac signals obtained from one or more implanted or externalelectrodes, such as surface electrodes and/or bipolar or unipolar atrialor ventricular implanted electrodes. The screen display also includesvarious icons, including an icon for starting/ending the threshold test.The threshold test is alternatively ended by removing the telemetrydevice 130 (e.g., wand) from near the implanted device 105 to interruptcommunication therebetween. In threshold testing mode this screendisplay also includes information regarding the particular chamber beingtested, the present amplitude of pace pulses being delivered (or thelast pacing amplitude before loss of capture, after the threshold testis ended), and/or the present pacing pulsewidth.

The above-described threshold testing technique provides only oneexample of carrying out a threshold test to determine pacing thresholds.In an alternative embodiment, the pacing energy is varied by decreasingpacing pulsewidths (the duration of the pacing pulse) rather than bydecreasing pacing amplitude. In another embodiment, either of amplitudeor pulsewidth are increased, rather than decreased, until capture isobtained. Moreover, it is understood that the caregiver can select whichelectrodes are associated with a particular pacing threshold test, sothat separate pacing thresholds are determined, for example, for atrial,ventricular, or other electrodes, or for unipolar or bipolar pacingconfigurations.

Returning to the above-described embodiment of decreasing pacingamplitudes to determine pacing threshold energies, it is apparent thatthe pacing threshold test is conducted “real time.” The accuracy of thedetermined pacing threshold depends on the caregiver ending thethreshold test when loss of capture is observed. However, otherdistractions, for example, may result in a less than adequate responsetime of the caregiver in ending the test. Moreover, proper medicalrecordkeeping may require that the physician records the test. For theseand other reasons, programmer 125 includes a printer that provides astrip chart recording of the threshold test. Furthermore, programmer 125also includes a screen display that also displays the information thatis displayed by the recorded strip chart. In one embodiment, programmer125 also includes a storage device (e.g., magnetic disk storage) thatalso stores the same data that is recorded on the strip chart.

Example Recorded Output

FIG. 5 is an example of a strip chart recording provided by the printerassociated with programmer 125. Based at least in part on datatelemetered from implanted device 105 to external programmer 125, thestrip chart recording provides real time electrograms of cardiac signalsassociated with one or more implanted or surface electrode sites. In theembodiment illustrated in FIG. 5, the strip chart includes cardiacsignals from a surface electrogram 500, an atrial electrogram 505, and aventricular electrogram 510. These signals include cardiacdepolarizations that allow the caregiver to determine whether theparticular heart chamber has contracted in response to a delivered paceof a particular energy.

The strip chart of FIG. 5 also includes atrial and ventricular eventmarkers 515A-Z, indicated by upwardly pointing arrows. These arrowsindicate the occurrence of a pace, delivered by atrial therapy circuit310 or ventricular therapy circuit 320, or of a sensed cardiacdepolarization, detected by atrial sensing circuit 305 or ventricularsensing circuit 315. Below corresponding event markers, the strip chartincludes text describing information related to the particular eventmarker. “AS” indicates that the associated event marker corresponds toan atrial sense, “AP” indicates that the associated event markercorresponds to an atrial pace. Similarly, “VS” indicates that theassociated event marker corresponds to a ventricular sense, “VP”indicates that the associated event marker corresponds to a ventricularpace. Other markers also exist. A corresponding numeral indicates thetime interval in milliseconds since the previous event marker in thesame chamber. The strip chart of FIG. 5 also includes output indicators520A-J, based on data telemetered from the implanted device 105, of theenergies associated with particular pace pulses. In FIG. 5, becauseatrial amplitude is being varied to determine atrial pacing thresholds,the output indicators of atrial amplitudes are printed below theircorresponding event markers (e.g., output indicator 520A of 5.0Vcorresponds to atrial pace event marker 515F, output indicator 520B of5.0V corresponds to atrial pace event marker 515H, etc.). In oneembodiment, these output indicators of pacing amplitudes are alsodisplayed on a screen display of programmer 125. In a furtherembodiment, these output indicators of pacing amplitudes are also storeddigitally in storage media associated with programmer 125.

By providing a recorded representation of electrograms, pacing eventmarkers, and associated pacing amplitudes (or pulsewidths), thecaregiver is more easily able to determine the particular pacing energyat which capture is lost. The energy at which capture is lost isdetermined by locating the particular event markers which are notfollowed by a substantially immediate cardiac depolarization associatedwith the particular chamber of the heart to which the pacing energy isbeing delivered. The strip chart conveniently provides a representationof the pacing energy (e.g., amplitude or pulsewidth) that is easilyreferred to each corresponding pace, in this case, by being printeddirectly below the event marker associated with that pace. This recordedrepresentation of pacing energy makes it easy for the caregiver todetermine proper pacing thresholds to be used to ensure adequate pacing,while minimizing energy drain to prolong the useful life of implanteddevice 105.

FIG. 6 is an example of a strip chart recording, similar to FIG. 5, inwhich the output indicators 600A-J provide recorded indications ofpacing pulsewidth for a pacing threshold test that varies pacing energyby varying pacing pulsewidth, rather than amplitude. In FIG. 6, becauseatrial pacing pulsewidth is being varied to determine atrial pacingthresholds, the output indicators of atrial pulsewidth are printed belowtheir corresponding event markers (e.g., output indicator 600A of 0.5milliseconds corresponds to atrial pace event marker 515E, outputindicator 600B of 0.5 milliseconds corresponds to atrial pace eventmarker 515G, etc.).

In one embodiment, programmer 125 automatically selects the appropriateelectrogram (e.g., atrial or ventricular) to be displayed on the screendisplay of programmer 125 during the threshold test, based on theparticular chamber for which thresholds are being tested if thatelectrogram is not already being displayed on the screen display ofprogrammer 125. In another embodiment, the screen display of electrogramcorresponding to the chamber being tested for pacing thresholdsautomatically provides an enlarged view of that electrogram during thethreshold test of that chamber. This makes it convenient for thecaregiver to view small, not easily discernable evoked responseartifacts. This makes it easy, for example, for the physician to see ifa P-wave results from an atrial pace at a particular energy, otherwisethe P-wave may be quite difficult to see.

CONCLUSION

This document describes, among other things, portions of a cardiacrhythm management system including a user interface for performingtherapy energy threshold tests. In one embodiment, the user interfaceincludes recorded indications of the energy corresponding to pacedevents, so that the caregiver can easily determine the point at whichcapture was lost. This recorded representation of pacing energy makes iteasy for the caregiver to determine proper pacing thresholds to be usedto ensure adequate pacing, while minimizing energy drain to prolong theuseful life of the implanted device.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. For example, although aspects of the present system havebeen described with respect to threshold testing of pacing thresholds,it is understood that the user interface could provide similar usefuloperation during testing of defibrillation thresholds. In anotherexample, the recorded output indicator of therapy energy need not beprovided as a printed output; such recorded output can also be storedelectronically, such as together with corresponding electrograms andevent markers, for subsequent viewing on the screen display of theprogrammer or elsewhere. Other variations are also possible. The scopeof the invention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

1. A system comprising: an implantable medical device, the implantablemedical device comprising a processor and a device-readable medium, thedevice-readable medium comprising instructions, which when performed bythe processor, cause the implantable medical device to: deliver asequence of electrostimulation therapy instances; and communicateinformation about each instance included in the sequence to an externaluser interface, the information comprising information about theelectrostimulation energy including one or more of an electrostimulationpulse voltage, or an electrostimulation pulsewidth, for each instanceincluded in the sequence, such that the external user interface providesa plurality of concurrently-shown alphanumeric output indicators of theelectrostimulation energy including one or more of theelectrostimulation pulse voltage, or the electrostimulation pulsewidth,for each respective instance included in the sequence using theinformation received from the implantable medical device.
 2. The systemof claim 1, further comprising the external user interface, the externaluser interface including: a display monitor configured to display arespective indicator of one or more of the electrostimulation pulsevoltage, or the pulsewidth, in association with an indication of arespective instance of electrostimulation therapy delivered by theimplantable medical device; and a memory circuit configured to store therespective indicator of one or more of the electrostimulation pulsevoltage, or the pulsewidth, in association with an indication of therespective instance of electrostimulation therapy delivered by theimplantable medical device.
 3. The system of claim 2, wherein thedisplay monitor is configured to display a therapy marker correspondingto a respective instance of electrostimulation therapy delivered by theimplantable medical device.
 4. The system of claim 3, wherein theinstructions causing the implantable medical device to communicateinformation about each instance included in the sequence includeinstructions to communicate information about at least one of theindicator of electrostimulation pulse voltage, the pulsewidth, or atherapy marker, in association with each respective instance ofelectrostimulation therapy included in the sequence.
 5. The system ofclaim 2, wherein the external user interface comprises an inputconfigured to receive a command to vary the electrostimulation pulsevoltage; wherein the external user interface is configured to transmitthe command to vary the electrostimulation pulse voltage to theimplantable medical device; and wherein the device-readable mediumincludes instructions that cause the implantable medical device to varythe electrostimulation pulse voltages delivered during the sequence, inresponse to the command received by the input.
 6. The system of claim 2,wherein the external user interface comprises an input configured toreceive a command to vary the electrostimulation pulsewidth; wherein theexternal user interface is configured to transmit the command to varythe electrostimulation pulsewidth to the implantable medical device; andwherein the device-readable medium includes instructions that cause theimplantable medical device to vary the electrostimulation pulsewidthsdelivered during the sequence, in response to the command received bythe input.
 7. The system of claim 1, wherein the device-readable mediumcomprises instructions causing the implantable medical device tocommunicate a representation of a cardiac signal, acquired by theimplantable medical device, to the external user interface.
 8. Thesystem of claim 7, wherein the representation of the cardiac signalacquired by the implantable medical device includes the respectiveinstances of electro stimulation therapy included in the sequence; andwherein the device-readable medium comprises instructions causing theimplantable medical device to communicate information about one or moreof the electrostimulation pulse voltage, or the pulsewidth, inassociation with each respective instance of electrostimulation therapyincluded in the representation of the cardiac signal, acquired by theimplantable medical device, to the external user interface.
 9. Thesystem of claim 1, wherein the device-readable medium comprisesinstructions causing the implantable medical device to vary theelectrostimulation pulse voltage in correspondence to a specified seriesof amplitudes, during the delivery of the sequence.
 10. The system ofclaim 1, wherein the device-readable medium comprises instructionscausing the implantable medical device to communicate, on a beat-to-beatbasis, the information comprising the electrostimulation pulse voltagefor each instance included in the sequence, as the sequence is beingdelivered.
 11. The system of claim 1, wherein the information about eachinstance included in the sequence comprises information about theelectrostimulation pulse voltage for each instance included in thesequence, such that the external user interface provides a plurality ofconcurrently-shown alphanumeric output indicators of theelectrostimulation pulse voltage for each respective instance includedin the sequence using the information received from the implantablemedical device.
 12. The system of claim 1, wherein the information abouteach instance included in the sequence comprises information about theelectrostimulation pulsewidth for each instance included in thesequence, such that the external user interface provides a plurality ofconcurrently-shown alphanumeric output indicators of theelectrostimulation pulsewidth for each respective instance included inthe sequence using the information received from the implantable medicaldevice.
 13. A method, comprising: delivering a sequence ofelectrostimulation therapy instances using an implantable medical deviceincluding a processor, the sequence delivered under the control of theprocessor according to instructions provided by a device-readablemedium; communicating information about each instance included in thesequence from the implantable medical device to an external userinterface, the information comprising information about theelectrostimulation energy including one or more of an electrostimulationpulse voltage, or an electrostimulation pulsewidth, for each instanceincluded in the sequence, such that the external user interface providesa plurality of concurrently-shown alphanumeric output indicators of theelectrostimulation energy including one or more of theelectrostimulation pulse voltage, or the electrostimulation pulsewidth,for each respective instance included in the sequence using theinformation received from the implantable medical device.
 14. The methodof claim 13, further comprising displaying the concurrently-shownalphanumeric output indicators including one or more of theelectrostimulation pulse voltage, or the electrostimulation pulsewidth,for each respective instance included in the sequence using theinformation received from the implantable medical device, eachconcurrently-shown indicator displayed in association with an indicationof a respective instance of electrostimulation therapy delivered by theimplantable medical device.
 15. The method of claim 14, comprisingdisplaying a therapy marker corresponding to a respective instance ofelectrostimulation therapy delivered by the implantable medical device.16. The method of claim 15, comprising communicating, from theimplantable medical device to the external user interface, informationabout at least one of the indicator of electrostimulation pulse voltage,the pulsewidth, or a therapy marker, in association with each respectiveinstance of electrostimulation therapy included in the sequence.
 17. Themethod of claim 13, comprising receiving a command to vary theelectrostimulation pulse voltage using an input provided by the externaluser interface; transmitting the command to vary the electrostimulationpulse voltage to the implantable medical device; and in response to thecommand, using the implantable medical device, varying theelectrostimulation pulse voltages during the sequence.
 18. The method ofclaim 13, comprising receiving a command to vary a electrostimulationpulsewidth using an input provided by the external user interface;transmitting the command to vary the electrostimulation pulsewidth tothe implantable medical device; and in response to the command, usingthe implantable medical device, varying the electrostimulationpulsewidths delivered during the sequence.
 19. The method of claim 13,comprising: acquiring a cardiac signal using the implantable medicaldevice; communicating a representation of the acquired cardiac signal tothe external user interface using the implantable medical device, therepresentation of the cardiac signal acquired by the implantable medicaldevice including the respective instances of electrostimulation therapyincluded in the sequence; and communicating information about one ormore of the electrostimulation pulse voltage, or the pulsewidth, inassociation with each respective instance of electrostimulation therapyincluded in the representation of the cardiac signal acquired by theimplantable medical device, to the external user interface, using theimplantable medical device.
 20. The method of claim 13, comprisingvarying the electrostimulation pulse voltage according to specifiedamplitude increments, during the delivery of the sequence.
 21. Themethod of claim 13, comprising communicating, from the implantablemedical device to the external user interface, on a beat-to-beat basis,the information comprising the electrostimulation pulse voltage for eachinstance included in the sequence, as the sequence is being delivered.22. A system comprising: an implantable medical device, the implantablemedical device comprising a processor and a device-readable medium, thedevice-readable medium comprising instructions, which when performed bythe processor, cause the implantable medical device to: deliver asequence of electrostimulation therapy instances using an implantablemedical device; communicate from the implantable medical device to anexternal user interface, on a beat-to-beat basis, information about oneor more an electrostimulation pulse voltage, or an electrostimulationpulsewidth, for each instance included in the sequence, as the sequenceis being delivered, such that an external user interface provides aplurality of concurrently-shown alphanumeric output indicators of one ormore of the electrostimulation pulse voltage, or the pulsewidth, foreach respective instance included in the sequence, using the informationreceived from the implantable medical device.